This invention relates generally to compressor blades, and specifically, to the provision for an undercut radially inward of the leading edge of the airfoil portion of the blade.
In large gas turbines used for generating electricity, power companies regularly water wash the machines as soon as any performance degradation is noticed. The water wash is sprayed into the machine at the compressor end, near the hub, and the fluid is flung out into the flow path, cleaning the compressor blades. As a result of this water wash, the first stage blades experience significant erosion along their leading edges, especially at the hub of the airfoil, i.e., where the airfoil meets the platform. This leading edge erosion reduces the high cycle fatigue capability of the material and, in the presence of vibratory excitation, may lead to blade failure.
Accordingly, there is a need to create a more erosion tolerant blade by lowering the mean and vibratory stress at the leading edge of the airfoil portion of the blade.
In accordance with an exemplary embodiment of this invention, attachment material (i.e., material in the root portion of the blade used to secure the blade to the compressor rotor or wheel) directly below, or radially inward of, the blade leading edge is removed. This creates an undercut below the blade platform and the leading edge of the blade. In other words, the blade leading edge and the front of the blade platform overhangs the attachment portion. The gap or space created by the material removal may be filled, if necessary, with a discrete spacer. The undercut arrangement effectively unloads the leading edge of the blade, thereby reducing the local mean and vibratory stresses along the leading edge.
Accordingly, in its broader aspects, the present invention relates to a compressor blade comprising an airfoil portion having a leading edge, a radially inner attachment portion, and a platform between the airfoil portion and the attachment portion, wherein material is removed from the attachment portion to form an undercut at a front face thereof to thereby provide an overhang radially inward of the platform and leading edge of the airfoil portion.
In another aspect, the invention relates to a compressor blade comprising an airfoil portion having a leading edge, a radially inner attachment portion, and a platform between the airfoil portion and the attachment portion, wherein material is removed from the attachment portion to form an undercut at a front face thereof to thereby provide an overhang radially inward of the platform and leading edge of the airfoil portion; wherein, when assembled on a compressor wheel, a void created by the undercut is filled by a spacer; and wherein the undercut has a depth of from about 0.5xe2x80x3 to about 1.0xe2x80x3.
In still another aspect, the invention relates to a method of unloading a leading edge of an airfoil portion of a compressor blade comprising: a) providing a blade having an airfoil portion with a leading edge, a platform, and an attachment portion adapted to secure the blade to a compressor wheel; and b) removing material from the attachment portion to create an undercut radially inward of the leading edge of the airfoil portion.
The invention will now be described in conjunction with the single drawing FIGURE identified below.